ctypes从c函数返回一个字符串 [英] ctypes return a string from c function

问题描述

我是Python的资深人士，但对C的涉猎却不多。半天没在网上找到对我有用的任何东西之后，我想我会在这里问问题并获得所需的帮助。

我想做的是编写一个简单的C函数，该函数接受一个字符串并返回另一个字符串。我打算用几种语言（Java，Obj-C，Python等）绑定此函数，所以我认为它必须是纯C语言？

这就是我所拥有的至今。注意，尝试在Python中检索值时遇到段错误。

hello.c

  #include< stdlib.h> 
 #include< stdio.h> 
 #include< string.h> 
 
 const char * hello（char * name）{
 static char greeting [100] = Hello，; 
 strcat（问候，名字）; 
 strcat（问候，！\n）; 
 printf（％s\n，问候）； 
返回问候语； 
} 
  

main.py

 导入ctypes 
 hello = ctypes.cdll.LoadLibrary（'./ hello.so'）
 name = Frank 
 c_name = ctypes。 c_char_p（name）
 foo = hello.hello（c_name）
 print c_name.value＃可以正常返回
 print ctypes.c_char_p（foo）.value＃segfault 
  

我读到段错误是由C释放最初为返回的字符串分配的内存引起的。也许我只是在吠错一棵树？

完成我想要的东西的正确方法是什么？

解决方案

在hello.c中，您将返回一个本地数组。您必须返回一个指向数组的指针，该数组必须使用malloc动态分配。

  char * hello（char *名称）
 {
 char hello [] = Hello; 
 char excla [] =！\n; 
 char * greeting = malloc（sizeof（char）*（strlen（name）+ strlen（hello）+ strlen（excla）+ 1））; 
 if（greeting == NULL）exit（1）; 
 strcpy（问候，你好）; 
 strcat（打招呼，名字）; 
 strcat（打招呼，不打扰）; 
返回问候语； 
} 
  

I'm a Python veteran, but haven't dabbled much in C. After half a day of not finding anything on the internet that works for me, I thought I would ask here and get the help I need.

What I want to do is write a simple C function that accepts a string and returns a different string. I plan to bind this function in several languages (Java, Obj-C, Python, etc.) so I think it has to be pure C?

Here's what I have so far. Notice I get a segfault when trying to retrieve the value in Python.

hello.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

const char* hello(char* name) {
    static char greeting[100] = "Hello, ";
    strcat(greeting, name);
    strcat(greeting, "!\n");
    printf("%s\n", greeting);
    return greeting;
}

main.py

import ctypes
hello = ctypes.cdll.LoadLibrary('./hello.so')
name = "Frank"
c_name = ctypes.c_char_p(name)
foo = hello.hello(c_name)
print c_name.value # this comes back fine
print ctypes.c_char_p(foo).value # segfault

I've read that the segfault is caused by C releasing the memory that was initially allocated for the returned string. Maybe I'm just barking up the wrong tree?

What's the proper way to accomplish what I want?

解决方案

In hello.c you return a local array. You have to return a pointer to an array, which has to be dynamically allocated using malloc.

char* hello(char* name)
{ 
    char hello[] = "Hello ";
    char excla[] = "!\n";
    char *greeting = malloc ( sizeof(char) * ( strlen(name) + strlen(hello) + strlen(excla) + 1 ) );
    if( greeting == NULL) exit(1);
    strcpy( greeting , hello);
    strcat(greeting, name);
    strcat(greeting, excla);
    return greeting;
}

这篇关于ctypes从c函数返回一个字符串的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！